100 BRITISH BELEMNITES. 
BELEMNITES QuINQUESULCATUS. PI. XXIII, fig. 56; Pl. XXIV, fig. 57. 
Reference. Belemnites quinquesulcatus, Blainville, ‘Mém. sur Bélemn.,’ p. 83, pl. ii, 
fig. 8, 1827. 
B. compressus, Sowerby, ‘ Min. Conch.,’ pl. 590, fig. 4, 1828. 
Guarp. Sheath large, conical, compressed, smooth. Anterior region unknown. 
Alveolar region conoid. Apicial region rapidly tapering to an obtuse compressed summit, 
and grooved with four, five, or six furrows, viz. two latero-dorsal extending over about 
one third of the apicial region, two latero-ventral of about half that length, one medio- 
dorsal, and one medio-ventral of variable length and distinctness. 
The sections of the sheath vary according to situation. At the alveolar apex the con- 
tour is nearly elliptical, with diameters as 90 to 100; within the border the layers are oval 
(the ventral region broadest), while nearer the centre the layers show inflexions correspond- 
ing to the grooves of the summit, though still nearer the axis these are again lost. Nearer 
the summit the contour consists of two unequal subcircular curves, and the plan of the 
summit is a compressed pentagonal or hexagonal figure, with four, five, or six deep notches. 
When the sheath is broken across the central layers sometimes separate from the rest, so 
as to appear in a fluted prominence, and the same thing happens in old specimens from 
decay. Substance light-brown or grey. 
Greatest length observed 8 inches, with a diameter not exceeding 2 inches. 
Proportions. The ventro-dorsal diameter at the alveolar apex being 100, the ventral 
radius is 43, the dorsal 57 ; the transverse diameter is 87. 
Puracmocone. Oblique, deeply inserted, with straight sides inclined at angles of 
23° and 27°. Section compressed elliptical in the ratio of 87 to 100. The ventral region 
occupies about half the circumference. The septa are very oblique, advancing dorsally, 
not waved on the edge nor undulated by the siphon. Irregular striz are seen parallel 
to the ventral line, crossing cthers parallel to the edges of the septa. On the dorsal 
aspect are arched shades of colour crossing the contrary curvatures of the striz of growth. 
The ventral aspect is often black. 
Proportions. Diameters as 100 to87. Depth of chambers one eighth of the diameter. 
Varieties, ‘The degree in which the figure approaches to a cone varies a little, and 
the apicial furrows are rather inconstant. Some specimens show hardly any medio- 
ventral or medio-dorsal grooves, in others these are distinct or even duplicate, and the 
intervening spaces are striated. 
Localities. In the Lower Oolite formation of Yorkshire, at White Nab, Cloughton 
Wyke, Carlton Husthwaite. (Also near Meziéres, Blainville.) At Sherborne, in Dorset 
